Can't remove object via python once grouped
So, I submitted a bug report, and got a same day response from Bastien. Turns out, the problem is related to the Fake User restructuring that is going on and there isn't a straightforward way to do it. Here's a link to the bug report: Blender Bug Tracker

He also pointed me in the direction of an effective workaround that I thought I'd share. Here is the working code:

import bpy

scn = bpy.data.scenes['Scene']
ob = bpy.data.objects['Cube']

testgroup = bpy.data.groups.new('testgroup')
testgroup.objects.link(ob)
testgroup.objects.unlink(ob)

scn.objects.unlink(ob)

ob.user_clear()    #manually clears all users, frees the object to be removed

bpy.data.objects.remove(ob)